Radio propagation is often limited by multipath fading, which is typically characterized by antenna position dependant phase and amplitude variations. To mitigate these fades, antenna diversity is commonly used were a receiver can select an antenna that provides the highest signal quality.
Conventional Antenna Diversity receivers are typically optimized to perform in a synchronized fashion. One examples of a conventional receiver is Advanced Antenna Diversity Mechanism by Qun Shen and Michael Lenzo, U.S. Pat. No. 5,952,963 issued Sep. 14, 1999 (“Chen”). Another example is Network utilizing modified preamble that supports antenna diversity by Ronald L. Mahany, U.S. Pat. No. 6,018,555 issued Jan. 25, 2003 (“Mahany”). By maintaining a timer the receiver knows when to start reception and can immediately start to assess the signal quality. After that the receiver switches to another antenna and again assesses the signal quality. The antenna that reveals the highest quality is finally selected to receive the remainder of the packet. In Chen, Time Division Multiple Access (TDMA) technology is employed. Referring to FIG. 1 of Chen, the receiver is synchronized according to the TDMA time slots and using this synchronization it identifies received packet message fields such as the preamble 16, synch word 18, data field 20, and the CRC, and it assesses the signal quality corresponding to those fields, for example using Receive Signal Strength Indicators RSSI0 10 and RSSI 1 12. Comparator 14 outputs the selection. In Mahany, the preamble contains multiple portions. The preamble portions are identified by the receiver and the quality is assessed for each. In both references, the antenna selection relies on the receiver's knowledge of where certain fields are in the received message due to the synchronous timing relationship between the received packet and a timing reference in or available to the receiver.